1. Field of the Invention
The invention relates to a microphone module with electromagnetic interference (EMI) shielding means.
2. Description of the Prior Art
Referring to FIGS. 1A, 1B, and 1C, a conventional condenser microphone module 100 comprises a metal cabinet 110, a diaphragm 120, a plastic ring 130, a back plate 140, a conduction ring 142, and a substrate 150. The metal cabinet 110, closed at bottom by the substrate 150, accommodates the diaphragm 120, the plastic ring 130, the back plate 140, and the conduction ring 142. The diaphragm 120 and the back plate 140, spaced apart by the plastic ring 130, are permanently electrically charged to implement a capacitor sensor 160. Incoming sound waves enter via an acoustic opening 111 of the metal cabinet 110 and are translated into mechanical vibrations upon contacting the diaphragm 120. The mechanical vibrations are converted into an electrical signal that varies in voltage amplitude and frequency corresponding to the original sound waves. The substrate 150 generally is a circuit board with an integrated circuit chip 151 mounted thereon. The integrated circuit chip 151 receives and amplifies the electrical signal and provides an output signal.
The substrate (i.e. circuit board) 150 has a top surface 157 with the integrated circuit chip 151 mounted thereon, and a bottom surface 158 from which a plurality of pins 152, 154, 155, and 156 protruding. FIG. 2A depicts the top surface 157 of the substrate 150, wherein the shaded regions indicate a plurality of electrically conductive parts 1501, 1502, 1503, and 1504, and a shielding part 1505. FIG. 2B depicts the bottom surface 158 of the substrate 150, obtained by turning the substrate 150 in accordance with the arrow A of FIG. 2A. Except for the electrically conductive part 1501, the other electrically conductive parts 1502, 1503, and 1504, and the shielding part 1505 penetrate through the substrate 150 from the top surface 157 to the bottom surface 158.
The plurality of pins protruding from the bottom surface 158 of the substrate 150 respectively are a data pin 152, a power pin 154, a ground pin 155, and a clock pin 156. In operation, an external power source (not shown) provides the integrated circuit chip 151 with power through the power pin 154 on the bottom surface 158 and the electrically conductive part 1502 extending from the bottom surface 158 to the top surface 157. The integrated circuit chip 151 receives an electrical signal from the capacitor sensor 160 through the conduction ring 142 and the electrically conductive part 1501 on the top surface 157, receives a clock signal from external circuitry (not shown) through the clock pin 156 on the bottom surface 158 and the electrically conductive part 1503 extending from the bottom surface 158 to the top surface 157, and sends out a data signal through the electrically conductive part 1504 extending from the top surface 157 to the bottom surface 158 and the data pin 152 on the bottom surface 158.
The metal cabinet 110 is grounded and serves as an electromagnetic interference (EMI) shielding means for protecting the capacitor sensor 160 and the integrated circuit chip 151 from EMI. However, external electromagnetic waves may penetrate through the substrate 150 affecting the capacitor sensor 160 and the integrated circuit chip 151 in the condenser microphone 100. Specifically, the shielding part 1505 of the substrate 150 extending from the top surface 157 of FIG. 2A to the bottom surface 158 of FIG. 2B is grounded via the ground pin 155 and used for blocking the external electromagnetic waves. However, there is a gap not protected by the shielding part 1505, allowing electromagnetic waves to pass through. The gap is indicated by reference numeral 200 in FIG. 2C, which can be recognized when FIG. 2A is laid over FIG. 2B and both are observed simultaneously.